1. Field of the Invention
The present invention is related to a novel synthetic N-linked sialo-glycan-containing polymer having a polyglutamate backbone and an efficient method of producing the same.
2. Description of the Related Art
The influenza virus is one pathogen in which an effective treatment method or phylaxis method has not been discovered. Because the influenza virus has an extremely strong infectivity, antigen variation is repeated and a strain emerges with a different antigenicity until that point, there is a problem in that it is difficult to develop effective protection measures using a vaccine etc. Recently, there is growing concern with regards to the emergence of the human influenza virus which has its origins in the avian influenza virus. As a consequence, the development of an influenza virus absorbent or infection inhibitor for the prevention of the influenza virus is expected.
It is thought that infection of the influenza virus to a host cell is caused by hemagglutinin (HA) which is a surface protein of the virus recognizing and binding with sialic acid-containing glycoconjugates of the surface of the host cell as a receptor. It has been reported that the Influenza A virus which is isolated from Ayes preferentially binds with a glycan having NeuAc (α2,3) Gal at a terminal, however, the human virus which is extremely similar to this virus shows a very high binding affinity for a NeuAc (α2,6) Gal structure of the terminal.
In this way, because there are a variety of subtypes due to mutation in the influenza virus, a product is desired which has an anti-influenza effect which widely inhibits the binding of receptors regardless of the subtype of the virus as a more effective anti-influenza agent, and a sialic acid-containing glycan compound (sialo-glycan) is expected to be able to function as an infection inhibitor which inhibits binding to the virus receptor which is the first step of the influenza virus infection or as an influenza virus absorbent.
Conventionally, an attachment inhibition experiment of an influenza virus which uses hemagglutination inhibition activity as an index using various sialo-glycan compounds was performed. However, because the attachment inhibition activity of a virus is low or because the synthetic process is complex and impractical, an infection inhibitor of an influenza virus in which sialo-glycan is the active ingredient has still yet not been developed.
For example, a synthetic glycan polypeptide containing sialyl-N-acetyllactosamine with a molecular weight of 2,000-1,000,000 is disclosed in Japan Laid Open Patent 2003-73397 (patent document 1) and Glycobiology, 13, 315-326 (2003) (non-patent document 1), in which N-acetyllactosamine is introduced with a p-aminophenyl group as a linker to a side chain of the α-polyglutamic acid as α-polyglutamic acid backbone and further, a sialic acid is linked to the non-reducing terminal of the glycan, and it was confirmed as having an infection inhibition activity against a wide range of influenza virus isolated strains. This sialyl-N-acetyllactosamine binding synthetic glycan polypeptide is effective as an infection inhibitor or absorbent against the influenza virus, however, the raw material such as α-polyglutamic acid, N-acetylglucosamine derivative (p-nitrophenyl glycoside) is an expensive chemical compound, and the manufacturing process is also cumbersome requiring extremely high manufacturing costs, whereas, infection inhibition activity IC50 to the influenza virus 3-30 μg/ml is not a sufficient activity from a practical point of view.
In addition, a synthetic glycan polypeptide containing sialyl-N-acetyllactosamine in which the polypeptide part of the above stated synthetic glycan polypeptide containing sialyl-N-acetyllactosamine is converted into a γ-polyglutamic acid which can be obtained cheaply, or in which the linker part of the sialo-glycan part and the polyglutamic acid are converted into a cheap aminoalkylalcohol, is disclosed in International Laid Open Pamphlet, WO2007/02669 (patent document 2) and Bioorg. Med. Chem., 15, 1383-1393 (2007) (non-patent document 2), and it is reported that the obtained polymer has an inhibition activity of influenza virus infection tens of times greater compared to a conventional polymer.